A permanent magnet motor generally comprises a rotor with an even number of equally spaced, alternating polarity magnets situated around a periphery of the rotor, and a stator that holds a number of windings positioned around the rotor. DC current in the stator windings provides an electromagnetic field and the permanent magnets cause the rotor to move to align the magnetic forces produced by the magnets and the field.
A thin peripheral band is fitted over the rotor and magnets to reduce the flux harmonics in the air gap between the rotor and the stator.
An example of a permanent magnet generator using wedge-shaped permanent magnets is disclosed in U.S. Pat. No. 4,242,610. In this patent, the permanent magnets have a wedge angle which is critical to retaining the magnets in their slots.
Large permanent magnet rotors have diameters as large as three meters (3 m), which raise special problems in assembly, which are not resolved by the prior art.
First, handling the permanent magnet elements give rise to large undesirable magnetic forces. There is a need for additional tools to position the magnet elements during assembly and disassembly.
Second, an improved construction is needed for holding the magnets in place in large motors, once the rotors have been assembled.
The invention has been made to solve these problems, as well as to provide additional advantages.